As a first step toward the successful freeze-drying of nucleated mammalian cells, the resistance of bovine spermatozoa to freeze-drying will be studied. Semen samples will be cryoprotected by utilizing zwitterionic buffers and egg-yolk instead of glycerol. Glycerol has been shown to be the major obstacle to success in prior trials. Specimens will be lyophilized at controlled temperatures to various degrees of dehydration, with reconstitution in several liquids including zwitterionic buffers and seminal plasma. Cell damage will be assayed by measuring motility, acrosome damage, and enzyme release. Fertility of the reconstituted samples will be measured by insemination. The initial techniques will be improved and applied to other types of spermatozoa and other nucleated mammalian cells.